The present invention relates to an inductor element containing circuit board and a power amplifier module, and more particularly, to a circuit board structure which has an inductor element contained in a multi-layer circuit board.
In recent years, the proliferation of communication terminal devices represented by mobile telephones has resulted in an increased demand for power amplifier modules for use in transmitters in the micro-wave band. Such a power amplifier module is disposed in front of an antenna, for example, in a mobile telephone for performing a function of amplifying a signal outputted from a driver amplifier and delivering the amplified signal to the antenna, and generally comprises a three-stage amplifier circuit, an output matching unit, a second harmonic compensator, and the like.
Each stage of the amplifier circuit includes a semiconductor amplifier device such as FET, a matching circuit, a drain bias circuit, a gate bias circuit, and the like to form a complete circuit block. The output matching unit in turn is a circuit for matching the impedance in a frequency band intended for amplification (basic wave). in a frequency band used by the power amplifier module (for example, 880–915 MHz). The second harmonic compensator serves to prevent a second harmonic component from being delivered to the output because a frequency other than the basic wave delivered to the output can cause degraded characteristics of an associated communication terminal device.
For implementing a power amplifier module having the circuit configuration as described above, a laminate dielectric circuit board, for example, is used to form a matching circuit, a second harmonic compensator, part of an FET bias circuit (resistor, capacitor), a (λ/4) pattern of a bias circuit, and the like distributively in layers of the circuit board. Some of other resistors and capacitors are mounted on the circuit board using surface-mount type elements. Inductor elements are formed as conductor patterns on the layers of the circuit board. Semiconductor amplifier devices such as FET are directly mounted on the circuit board in the form of bare chip, or packaged in resin moldings for mounting on the circuit board.
JP-A-8-172161 and JP-A-2002-141757 disclose such a circuit board structure which comprises a power amplifier module or inductor elements.